Shunt for electric blasting caps



APi"il 6, 1943' R. B. SMITH 2,315,823v

` SHUNT FOR ELECTRIC BLASTING CAPS f Filed Nov. 2e, 19:58

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ATTORNEY Patented Apr. 6, 1943 UNITE Fi-CE 2,315,823 snUNr ron ELECTRICBLASTING cars Roscoe B. smith, Wilmington; no1., assignor to HerculesPowder Company; Wilmington, Del., a corporation of Delaware ApplicationNovember 26, iosa-serial No. 242,466

(o1. 1oz-f2s) 1 Claim.

My invention relates to improvement in blasting caps and otherelectrical ring devices for explosives. More particularly it relates tothe provision of means whereby the accidentalkflring of a blasting capor other electrical firing device through contact of the lead wires witha source of current will be positively avoided. Y

As is well known electric blasting caps comprise a container which holdsa detonating charge, for example, diazodinitrophenol. Within saidcontainer is provided a firing assembly which includes a bridge wireembedded within the detonating charge itself or within a more readilyred ignition charge. From the bridge wireA extend two insulated leadwires of such a. convenient length that they may be attached to a.source of electric current for the purpose of ring the said electricblasting cap. To facilitate the connection of these insulated lead wiresto the source of current it has been the accepted practice cf the priorart to furnish about two to about three inches of bare wire at the endsof said insulated lead wires.

It has been well recognized that the uninsulated portion of the leadwires constitute a hazard in that they afford an opportunity for theaccidental discharge of the cap by coming into contact with an electriccurrent. This accidental discharge is easily possible since, forexample, in a mine the lead wires are frequently trailed and are likelyto come into contact with a live circuit or a stray current as, forexample, a trolley line or a charged rail. To prevent the possibility ofpremature explosions, Various means of shunting the lead wires havebeenfsuggested, but have been for many reasons found unsatisfactory.

The methods of shunting now in use such as twisting the wires togetheror bridging the wires with various types of metal shunts, have not beenentirely satisfactory since in all cases the shunted wires are hard toseparate without considerable distortion or damage. This distortion ofthe bare ends of the lead wires makes their use diiiicuit as tightelectrical connections are harder to obtain.

The object of this invention is to provide means whereby thedifficulties of protecting electrical firing devices with metallicshunts are overcome.

A further object of this invention is to provide a shunting device forthe lead wires of electric ring devices that may be used and removedwithout distorting or damaging the bare ends of the lead wires.

Still a further object of this invention is the provision of a. metallicshunt that may be removed from and replaced on the bare ends of the leadwires of electric firing devices when it is desired to test the ringdevice before connection into the ring circuit. Other objects willappear hereinafter.

metallic spring clip of this invention provides due to its designpositive contact between the uninsulated portions of the two lead wiresof any'ring-device and thus prevents the accidental discharge of thedevice from contact of the lead wires with a strap currentv or a livecircuit. Further this metallic spring clip is very easy to place in-position on the lead wires and is equally easy to remove from the leadwires. The removal of the spring clip is carried out in such amannerthat the uninsulated portions of the lead wires are not damaged ordistorted in any way. The design of the clip aids the operator inplacing the clip on the bare ends of the wire at a point adjacent to theend of the insulated portion of the lead wires and further the design ofthe clip prevents the operator from placing the shunt on the insulatedportion of the lead wires. A shunt to be effective should be placedclosely to the end of the insulated portions of the lead wire but mustnot be on the insulation; therefore, the clip shunt of this inventionhas been so designed as hereinafter will be described to provide theserequirements of eectiveness.

Having now indicated in a general way the nature and purpose oi thisinvention there follows a more detailed description of preferredembodiments thereof as shown 'by the accompanying drawing in which:

Figure l shows an electric ring device in which the uninsulated endportions of the bundled lead wires are shunted by the metallic springclip of this invention.

Figure 2 shows a perspective view of the rnetallic spring clip shunt ofthis invention, this perspective view being an enlargement of themetallic spring clip shunt shown positioned on the wires of the firingdevice depicted in Figure l.

Figure 1 shows an electric blasting cap l from which extends a pair oflead wires of any common and well known size 2 that have theiruninsulated end portions 3 protected by the metallic spring clip shunt4. The clip shunt 4 is so placed on the lead wires that the bare ends 3are held in close contact. The rclip shunt of Figure l is shown inFigure 2 by a perspective View and is made of any metal that when formedas shown will have suicient spring to tend to maintain the open shapedepicted. The form of the shunt 4 provides two holes 5 and 6 which,preferably, have a tear-drop outline to insure maximum contact with thewires due to pressure and wedging. The holes 5 and 6 may be, however, ofany desirable size and shape. An insulation-stop hole "l, situated onlug 8, is of sufficient diameter to allow the insertion of theuninsulatedends 3 of the pair of lead wires 2, but is large enough-'topermit the passage, of the insulated portion ofthe leadwires 2. The@hole 9 situated at the bend of the clip 4 is ot such size and shape thatthe lead wires 2 may be inserted through it with ease. This hole 9 isprovided to allow the lead Wires of a firing device to pass completelythrough the shunt-thereby preventing the kinking of the wires. f

A modification of the design of the spring `clip shunt of this inventionomits the lug 8 with hole 'I thus removing the insulation-stop. Thismodication, therefore, necessitates the design and size of hole 6 to beso changed that the diameter 'will permit the passage of the uninsulatedportions 'of the lead wires butwill act as a stop to vthe insulatedportions of the wires. This modificat'ion further necessitates that thelead wires- '2 of the .device will' be threaded' through-fthey shunt`from the `end containing -hole1 9. It will be appreciated that I may,if so desired, design hole 9 to act asthe insulation stop. Now in theevent of desiring 'to thread the lead -Wires 2 through the shunt fromthe opposite end, that is through hole rst, the hole 5 will necessarilybecome the insulation-stop hole which will therebynecessitate a| changein the `diameter of hole 5.

It will be appreciated by'those skilled in the ar't vthat the design ofthis metallic clip shunt in respect to which hole is to be used as aninsuf lation-stop depends upon the method of threadl `the clip shown inthe attached drawings is parabolic, the spring section may be of anysuitable design that gives the necessary spring action to the slip.

The metallic clip shunt in accordance with this invention presentsseveralv very distinct advantages over the shunts of the prior art.

The insulation-stop hole presents an advantage since this hole providesthe means whereby an operator is aided in correctly locating the shunton the bare ends of the lead wires thereby ,preventing the improperapplication f of the shunt. The shunts of the prior art were placed inposition entirely by the skill of the operator and often a shunt waslocated partly or entirely onthe insulated portions of the-lead wires. Ashunt so located is rendered useless and becomes a hazard as the tiringdevice is left unprotected.

` A further advantage is the design of the clip shunt which prevents theaccidental removal of the device' as'its spring action provides positivel gripping of the wires and its slightly streamlined ,shape` preventsremoval by any brushing action."y The removal of shunt while dirlicultby accident is'v'eryeasy by an operator since a slight pressure on thesides of the shunt relieves all e gripping action' of the spring.

` v.Another advantage possessed by the shunt of this invention over anyshunt of the prior art is the fact that this shunt may be replaced onthe lead wires after its rst removal and still afford 'the sameefficient shunting action. This advantage is highly desirable since oneof the common practices in blasting is the removal of the shunt sometime before the actual firing of the device to allow testing of thefiring device by a blasting galvanometer or circuit tester. Thus, fromthe time of testing to the time of tiring there may elapse considerabletime and during the interval the' iiring device is unprotected. The useof a shunt capable of being replaced removes the necessity of leavingring devices unprotected.

The use of the clip shunt is also advantageous due to the condition inwhich this shunt leaves the wires of the firing device. The removal ofthe clip shunt from'the uninsulated portions of i the lead wires leavesthe wires in an undamaged and undistorted condition, and further duringremoval the clip shunt may also be allowed to exert'v a scraping actionon the lead wires and so provide clean, bright lead wire ends.Therefore,

lthe clip shunt of my invention aids materially in theI preparation ofpositive electrical connections to the firing circuit.

It will be understood that the metallic clip shunt in accordance withthis invention may be used as a protecting device on any of the electricring devices known to the art, for example electric blasting caps, delayelectric blasting caps, electric squibs, or any -other commercialelectric firing devices.,

It will furtherbe understood that the details and-examples givenhereinbefore are illustrative -Ionly and in no way limiting on myinvention as broadly described hereinbefore and in the ap- Vpendedclaim. Y

What I claim and desire to prot-ect by Letters Patent is:

For use with an electric detonator and its pair of lead wires, wheresaid lead Wires are of a size commonly used in electric detonators andbeing bare for a portion of their length at the outer ends and beinginsulated yfor the remainder of their length inwardly to the detonator,a portable shunt consisting of resilient conductive ma.- terial forshort-circuiting said lead Wires and adapted to be positioned on saidbare Wire portions immediately adjacent said insulated wire portions,said shunt comprising a resilient arcuately curved base portion having aperforation at the vortex thereof diametrically suiilcient to permitpassage therethrough of said insulated wire portions, diametricallyopposed resilient arms extending outwardly from said base portion inspaced relation to each other and being held in biased relationshiprelative to each other by means of said resilient base portion, theouter ends of each of said arms being bent at substantially right anglesinwardly toward each other to form a gripping element, the grippingelements being positioned in overlapping relation with each other, a lugstruck inwardly from one of said arms and positioned between and insubstantially parallel relation to said base portion and grippingelements, said lug and each of said gripping'elements having a wirereceiving aperture, the apertures being alignable in axial relation withsaid perforation to receive said pair of bare wire portions, saidapertures being of a diameter to permit passage of said pair of barewire portions and prevent passage of said pair of insulated wireportions thereby permitting automatic and positive positioning of saidshunt immediately adjacent said insulated wire portions on said barewire portions.

ROSCOE B. SMITH.

